linux-kernel - [PATCH v2] blk-mq: check on cpu id when there is only one ctx mapping

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Date:   Wed, 31 May 2023 16:38:29 +0800
From:   Ed Tsai <ed.tsai@...iatek.com>
To:     <axboe@...nel.dk>
CC:     <kbusch@...nel.org>, <liusong@...ux.alibaba.com>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        <peter.wang@...iatek.com>, <stanley.chu@...iatek.com>,
        <powen.kao@...iatek.com>, <alice.chao@...iatek.com>,
        <naomi.chu@...iatek.com>, Ed Tsai <ed.tsai@...iatek.com>
Subject: [PATCH v2] blk-mq: check on cpu id when there is only one ctx mapping

commit f168420 ("blk-mq: don't redirect completion for hctx withs only
one ctx mapping") When nvme applies a 1:1 mapping of hctx and ctx, there
will be no remote request.

But for ufs, the submission and completion queues could be asymmetric.
(e.g. Multiple SQs share one CQ) Therefore, 1:1 mapping of hctx and
ctx won't complete request on the submission cpu. In this situation,
this nr_ctx check could violate the QUEUE_FLAG_SAME_FORCE, as a result,
check on cpu id when there is only one ctx mapping.

Signed-off-by: Ed Tsai <ed.tsai@...iatek.com>
Change-Id: I4f95d7538532f72dcb20dacfdd639c97951c2729
---
 block/blk-mq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 41f7e2b500bd..ecc30ebe9483 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1176,7 +1176,8 @@ bool blk_mq_complete_request_remote(struct request *rq)
 	 * or a polled request, always complete locally,
 	 * it's pointless to redirect the completion.
 	 */
-	if (rq->mq_hctx->nr_ctx == 1 ||
+	if ((rq->mq_hctx->nr_ctx == 1 &&
+	     rq->mq_ctx->cpu == raw_smp_processor_id()) ||
 		rq->cmd_flags & REQ_POLLED)
 		return false;
 
-- 
2.18.0